1. Field of the Invention
This invention relates in general to liquid fueled combustion engines and in particular to a new means of preparing the fuel-air mixture for such systems. The invention is representatively applicable to, but not limited to, use with conventional liquid-fueled internal combustion engines.
2. Prior Art
Internal and external combustion engines (e.g. gasoline, diesel and Stirling engines) and other combustion devices, (e.g. heaters, boilers, turbines, etc.) provide a large percentage of the power requirements in the modern world; some common examples include the automobile engine, building heating systems, oil fired steam generators, etc. (Note: for brevity, such combustion systems will be referred to generally as "engines" for the rest of this document.) The vast majority of such devices are powered by liquid fuels. Of great importance in the design of such engines is the means used for mixing the liquid fuel with air (or other oxidizing gaseous mixture-hereafter "air" will be understood to include such gaseous mixtures) prior to burning this mixture in the combustion chamber of the engine.
In order to provide background information so that the invention may be completely understood and appreciated in its proper context, a brief description of the prior art in the field of fuel/air mixing in liquid fueled engines is here provided.
In the past, two primary methods of performing the fuel-air mixing process have dominated: carburation and fuel injection. Carburation has the advantages of simplicity, relatively low cost of manufacture, and low maintenance. Recently, performance, economic, and environmental concerns have brought fuel injection to the forefront of liquid fueled engine technology because fuel injection, with its greater control over the parameters of fuel/air mixing and delivery, provides the designer of combustion engines with greater options in optimizing fuel efficiency, engine control, power output, etc., while at the same time reducing polluting by-products from combustion.
Fuel injection systems create a fuel-air mixture by forcing liquid fuel through an orifice or nozzle into a mixing chamber where air is present. The mixing chamber may be: (1) an intake manifold (this is called "manifold injection"); (2) a cavity immediately outside the combustion chamber which is connected to the combustion chamber through a valved or unvalved passage ("port injection"); or (3) it may be the combustion chamber itself ("direct injection"--e.g. the diesel engine). In the case of multiple combustion chamber internal combustion engines, manifold injection typically employs one fuel injection device to service all cylinders. In the case of port and direct injection, of necessity there is one (or more) injection device(s) per cylinder.
With regard to timing, the injection of fuel may be continuous (called "continuous injection") or modulated in time ("called pulsed injection"). Pulsed injection, while more complicated and costly than continuous injection, allows for greater control of the parameters of mixing and delivering the fuel-air mixture, potentially enabling better optimization of combustion and overall operation of the engine or combustion system.
In summary then, regardless of particular design, all fuel injection systems (both prior art and the invention here described) are either of the "manifold", "port" or "direct" type (or some combination thereof). These types in addition are characterized as being either "continuous" or "pulsed".
Conventional fuel injection systems (i.e. the prior art) generally operate in one of two ways: (1) A high pressure fuel pump provides a flow of fuel under high pressure which is delivered to an orifice or nozzle. A valve (continuous or pulsed) controls the rate at which fuel is sprayed out of the orifice or nozzle into the mixing chamber. (2) A low pressure supply of fuel is directed to a positive displacement pump capable of producing high pressure. The pump provides a high pressure flow of fuel which is sprayed through an orifice, with a precisely controlled amount of fuel being expelled for each pumping cycle. The overall rate at which fuel is injected into the mixing chamber is controlled by altering the cycling rate of the pump and/or the displacement of the pump. Notice that in both designs, a high pressure, highly reliable pump is essential--and such a pump generally requires high precision, costly manufacture. In configuration (1), the production of fuel pressure and the metering of the injection rate are separate functions, performed by the pump and the valving respectively; in configuration (2) these functions are combined. Notice also that in order to achieve timed fuel injection, in configuration (1) a rapidly responding valve system must be provided; to achieve timed fuel injection in configuration (2) the pump must be capable of having both its displacement and its cyclic rate of operation rapidly varied. These requirements result in increased system complexity, with its attendant costs.
Regardless of the precise merits, features, and advantages of the prior art, none of them achieves or fulfills the purposes of the present invention, as the description given below will make apparent. Among the disadvantages of conventional fuel injection are the following: (1) A high degree of mechanical complexity, with the accompanying increase in possible modes of failure; (2) High cost of manufacture and maintenance due to the complexity of the systems; (3) Safety hazards due to the use of high pressure fuel pumps in most conventional fuel injection systems. In automotive applications, for example, the rupture of a high pressure fuel line due to a collision or other failure presents a serious fire hazard--and expensive safety systems must be employed to guard against this danger. (4) Conventional fuel injection systems are "analog" in nature, requiring some kind of digital-to-analog interface in order to allow computer control. These problems of conventional fuel injection have tended to prevent its universal adoption despite its many advantages.